This invention was made in the course of, or under, a contract with the United States Department of Energy. It relates in general to long range ordered alloys of the transition metals V, Ni, Co, and Fe and more specifically to long range ordered alloys of the AB.sub.3 type.
Long range ordered alloys are like intermetallic compounds whose atoms are arranged in order below a critical ordering temperature, T.sub.C. The term "long range order" refers to alloys having ordered structure extending for a distance of more than 100 atoms in a single domain. The principle advantage of long range ordered alloys is their strength and stability in use environments at high temperatures. At temperatures below T.sub.C the ordered structure of the alloy has the lowest free energy. An ordered alloy can experience temperatures below T.sub.C for indefinite periods without undergoing significant compositional or phase changes. Above T.sub.C, the tensile strength of ordered alloys is substantially reduced due to the disordering effect.
In the prior art the principal disadvantage associated with long range ordered alloys has been their extreme brittleness. As a result long range ordered alloys are not used as structural material for high temperature applications.
Long range ordered alloys have been found in the V--Co--Fe system. The crystal structure of an alloy of the composition V(Fe.sub.0.17, Co.sub.0.83).sub.3 is described in an article entitled "Influence of Radius Ratio on the Structure of Intermetallic Compounds of the AB.sub.3 Type" by Van Vucht in J. Less-Common Metals, 11, (1966) 308-322. The structures of alloys of the compositions V(Fe.sub.0.3, Co.sub.0.7).sub.3, V(Fe.sub.0.1, Co.sub.0.9).sub.3 and V(Fe.sub.0.03, Co.sub.0.97).sub.3 are described in an article entitled "Close-Packed Ordered AB.sub.3 Structures in Ternary Alloys of Certain Transition Metals" by Sinha, in Transactions of the Metallurgical Society of AIME, 25, May, 1969, 911-917. Apparently neither author studied the mechanical properties of the cast alloys and it can be presumed that the alloys were thought to be excessively brittle as are other ordered alloys of the AB.sub.3 structure. Additionally, neither author described the effect of Fe content on T.sub.C.